You fellers are a scaren me. Well, not really.
I have a .300 BlackOut and I don't find the cost to load all that much more than a .223/5.56.
I am a pack rat and have been for more years than I want to say. I dug through all of my old dead brass and pulled out all of the .223/5.56 stuff with split mouths and crushed necks and the like. Checked the heads and bodies over, tossing back the undesirables. Chopped them off with a saw, sized them and trimmed to length. I have brass, same price as what it is .223/5.56 stuff. See below.
Primers are the same.
Bullets are not the same. But, being a tightwad, I don't go crazy. I've loaded 220 grainer, (see below) 150 (147) grain GI pulls, 150 grain nice bullets (to hunt with), some expensive 125 grain OTMs and a lot of 110 grain V-Maxs. Compared to .224 bullets, the 30 cals are a little more. Sorry, haven't found any of the other bullets.
Powder... Different powders and amounts for both. From 16.2gr to 20.0gr of H110 (147gr to 110gr bullets) compared to my normal loadings of 25.5gr to 26.6gr of 748 for 50gr and 55gr .224 bullets.
So the only big change is the price of the bullets. Powder is actually less cost per load.
Course, I load all of my own and if my desire is to just go bang a lot, well a .22RF does that and I don't.
The 220gr slugs (right photo) went into an old cedar log and I was able to dig them out.
I like the .300 BlackOut. It doesn't replace my 308/7.62 or .223/5.56. They all have a place and fill them well.